1. Field of the Invention
The present invention relates to the coatings for medical devices and, more particularly, to apparatus and methods using ultrasound energy for mixing two or more different liquids and coating any medical device surfaces. The term “medical device” as used in this application includes stents, catheters, synthetic blood vessels, artificial valves or other similar devices amenable and benefited from spray coating. For clarity, understandability and by way of example, the term “stent” in this application is used interchangeably with the term “medical device”.
2. Background of the Related Art
A stent is a generally small, cylindrical shaped, mesh tube that is inserted permanently into an artery. A stent helps hold open an artery so that blood can flow through it. Stents can generally be divided into two categories: a) Metallic Bare Stents; and b) Drug Eluting Stents. Drug-eluting stent contain drugs that potentially reduce the chance the arteries will become blocked again.
The stents are generally tubular in design made up of fine mesh and/or wire having a small diameter and defining a large number of narrow spaces between various components. Frequently, stents are coated with a range of materials utilizing various methodologies and for various reasons. Because of their specific construction, designs and materials, uniformly coating the inner and outer surfaces of the stent, repeatably with no webbing, stringing and with controllable dosage of drug-polymer coating has been problematic.
Examples of patents disclosing stents include U.S. Pat. No. 4,739,762 by Palmaz; U.S. Pat. No. 5,133,732 by Wiktor; U.S. Pat. No. 5,292,331 by Boneau; U.S. Pat. No. 6,908,622 by Barry et al.; U.S. Pat. No. 6,908,624 Hossayniy et al.; and U.S. Pat. No. 6,913,617 by Reiss.
There are a variety of U.S. Published Patent Applications related to stent coatings, including, for example: U.S. Pat. Pub. No. 2003/0225451 A1 by Sundar; U.S. Pat. Pub. No. 2004/0215336 A1 by Udipi, et al.; U.S. Pat. Pub. No. 2004/0224001 A1 by Pacetti, et al.; U.S. Pat. Pub. No. 2004/0234748 A1 by Stenzel; U.S. Pat. Pub. No. 2004/0236399 A1 by Sundar; and U.S. Pat. Pub. No. 2004/0254638 A1 Byun.
According to above-mentioned patents and applications, the coating have been applied to the surface of stents from both inside and outside by different methods, such as mechanical coating, gas spray coating, dipping, polarized coating, electrical charge (electrostatic) coating, ultrasound coating, etc. Some of them like U.S. Pat. No. 6,656,506 utilize a combination of dipping and spraying). Several of them utilize the ultrasound energy, such as, for example, U.S. Pat. No. 6,767,637; and U.S. Pat. Pub. No. 2005/0064088 for ultrasound spraying. In another method, U.S. Pat. No. 5,891,507 discloses coating the surface of a stent by dipping in ultrasonic bath.
Despite these coating technologies and methods, these related technologies have numerous shortcomings and problems. For example, non-uniformity of coating thickness, webbing, stringing, bare spots on the stent surface, drug wasting, over spray, difficulties with control of drug flow volume, adhesive problems, long drying time and a need sterilization/sanitation, among others.
Ultrasonic sprayers (U.S. Pat. Nos. 4,153,201, 4,655,393, and 5,516,043) typically operate by passing liquid through the central orifice of the tip of an ultrasound instrument. Known applications include the use of a gas stream to deliver aerosol particles to coating surface. Prior art systems are being used for ultrasonic stent coating by delivering aerosol particles via air jet or gas stream.
Among prior gas ultrasound sprayers are wound treatment applications (U.S. Pat. Nos. 5,076,266; 6,478,754; 6,569,099; 6,601,581; 6,663,554), which are creating the spray. USSR patent #1237261, issued for Babaev in 1986 can mix the different liquids outside of the ultrasound transducer tip.
Typically, stents need to be coated with a drug and/or polymer in a single layer. Current techniques require the drug or polymer be mixed before coating. This can lead to timing issues such as when a polymer is polymerizes after mixing.
Accordingly, there is a need for a method and device for mixing two or more different drugs with the polymers and defect-free, controllable coating process of the stents.